A hydraulic self starting system has to release the stored energy in an accumulator or other source under high pressure via a start valve to the starter motor which subsequently turns the engine to achieve self ignition at the engine. To restore the energy the accumulator, if an accumulator is used, is recharged by an engine driven pump through an automatic recharge valve. If for whatever reason the stored energy is exhausted before the engine has fired, the energy can be restored by means of a manual hand pump, which is not possible in the commonly used electrical starting system. This is one of the great advantages of the hydraulic starting systems.
In these systems the more commonly known starter motor valves impose high shockloads during the initial part of the engine cranking cycle. This is the result of extremely rapid acceleration of the starter motor, which once it has engaged with the engine flywheel ring gear, is momentarily brought to a halt until the inertia of the engine is overcome and the engine and starter motor rotate together. These shock loads can result in premature failure of starter pinion gear and engine ring gear.